System and method for focus control in extreme ultraviolet lithography systems using a focus-sensitive metrology target

ABSTRACT

A focus-sensitive metrology target may be formed and read-out by a fabrication tool. A resulting overlay signal may be translated into a focus offset by comparison to a previously-determined calibration curve. One or more translated signals may be fed back to the fabrication tool for focus correction or used for prediction of on-device overlay (correction of overlay metrology results). In one embodiment, focus and overlay may be measured using a single target, where one portion of the target is formed on a first layer and includes a focus-sensitive design, and where another portion of the target is formed on a second layer and includes a relatively less focus-sensitive design. In some embodiments, a relative difference in focus response may be used to estimate an impact of focus error on device overlay and calculate non-zero offset contributions.

TECHNICAL FIELD

The present disclosure is related generally to focus control in extremeultraviolet lithography process using focus-sensitive metrology targets.More specifically, the present disclosure relates to correction offocus-induced overlay metrology target-to-device errors.

BACKGROUND

Focus control in EUV lithography is increasingly important, due tonon-overlapping process windows for different structures (e.g., 3D maskeffects). Moreover, random defects strongly increase in density whenmoving out of best focus, which further reduces the usable focus window.Additionally, the generation of defects and focus errors in EUVlithography are known to cause critical dimension (CD) errors as well aspattern placement errors (PPE). However, such PPE may also have rootcauses other than focus errors. It is thus desirable to have fast andhigh-accuracy methods available to independently measure focus errors aswell as PPE in EUV lithography. Additionally, the size of metrologytarget features continues to decrease with evolving metrology methodscapable of controlling focus and overlay within tighter specifications.Moreover, existing methods of focus control are generally incompatiblewith focus and overlay metrology using a single target (e.g., correctionof focus-induced overlay metrology errors using one or more focusmeasurements).

Accordingly, it may be desirable to provide a system and method forfocus control using a focus-sensitive metrology target.

SUMMARY

A focus-sensitive metrology target is disclosed, in accordance with oneor more embodiments of the present disclosure. In one embodiment, thefocus-sensitive metrology target may include a first set of first targetstructures formed along a y-direction on one or more layers of a sample,the first set of first target structures comprising a plurality ofsegmented first pattern elements. In another embodiment, thefocus-sensitive metrology target includes a first set of second targetstructures formed along a y-direction on one or more layers of thesample, the first set of second target structures comprising a pluralityof segmented second pattern elements.

A system is disclosed, in accordance with one or more embodiments of thepresent disclosure. In one embodiment, one or more controllers havingone or more processors communicatively coupled to one or morefabrication tools, wherein the one or more processors are configured toexecute a set of program instructions maintained in memory, and whereinthe set of program instructions is configured to cause the one or moreprocessors to: receive, from one or more portions of one or morefabrication tools, one or more signals indicative of illuminationemanating from a first set of first target structures and a first set ofsecond target structures of one or more focus-sensitive metrologytargets of a sample, wherein the one or more focus-sensitive metrologytargets of the sample comprise: a first set of first target structuresformed along a y-direction on one or more layers of a sample, the firstset of first target structures comprising a plurality of segmented firstpattern elements; and a first set of second target structures formedalong a y-direction on one or more layers of the sample; determine oneor more focus-offset values based on the one or more signals indicativeof illumination emanating from the first set of first target structuresand the first set of second target structures; and provide one or morefocus corrections based on the one or more focus-offset values to one ormore portions of the one or more fabrication tools.

A method of measuring overlay is disclosed, in accordance with one ormore embodiments of the present disclosure. In one embodiment, themethod includes illuminating a sample having one or more focus-sensitivemetrology targets. In another embodiment, the method includes detecting,in one or more metrology modes, one or more signals indicative ofillumination emanating from one or more portions of the one or morefocus-sensitive metrology targets, wherein the one or morefocus-sensitive metrology targets of the sample comprise a first set offirst target structures formed along a y-direction on one or more layersof a sample, the first set of first target structures comprising aplurality of segmented first pattern elements; and a first set of secondtarget structures formed along a y-direction on one or more layers ofthe sample. In another embodiment, the method includes generating one ormore overlay measurements based on the one or more signals indicative ofillumination emanating from the one or more portions of the one or morefocus-sensitive metrology targets. In another embodiment, the methodincludes determining an overlay error between two or more layers of thesample based on the one or more overlay measurements.

A method of forming a focus-sensitive metrology target is disclosed, inaccordance with one or more embodiments of the present disclosure. Inone embodiment, the method includes forming a first set of first targetstructures along a y-direction on one or more layers of a sample, thefirst set of first target structures comprising a plurality of segmentedfirst pattern elements. In another embodiment, the method includesforming a first set of second target structures along a y-direction onone or more layers of the sample, the first set of second targetstructures comprising a plurality of segmented second pattern elements.

BRIEF DESCRIPTION OF DRAWINGS

The numerous advantages of the disclosure may be better understood bythose skilled in the art by reference to the accompanying figures.

FIG. 1A is a top view of a focus-sensitive metrology target, inaccordance with one or more embodiments of the present disclosure.

FIG. 1B is a top view of a focus-sensitive metrology target, inaccordance with one or more embodiments of the present disclosure.

FIG. 1C is a top view of a focus-sensitive metrology target, inaccordance with one or more embodiments of the present disclosure.

FIG. 1D is a top view of a focus-sensitive metrology target, inaccordance with one or more embodiments of the present disclosure.

FIG. 2 is a conceptual view of one or more portions of a focus controlsystem, in accordance with one or more embodiments of the presentdisclosure.

FIG. 3 is a schematic view of focus control system, in accordance withone or more embodiments of the present disclosure.

FIG. 4 is a process flow diagram depicting the steps of a method offocus control, in accordance with one or more embodiments of the presentdisclosure.

FIG. 5 is a process flow diagram depicting the steps of a method ofselecting one or more metrology target designs as part of a focuscontrol method, in accordance with one or more embodiments of thepresent disclosure.

FIG. 6 is a process flow diagram depicting the steps of a method ofdetermining one or more focus errors as part of a focus control method,in accordance with one or more embodiments of the present disclosure.

FIG. 7 is a process flow diagram depicting the steps of a method ofmeasuring overlay, in accordance with one or more embodiments of thepresent disclosure.

FIG. 8 is a process flow diagram depicting the steps of a method offorming a focus-sensitive metrology target, in accordance with one ormore embodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure has been particularly shown and described withrespect to certain embodiments and specific features thereof. Theembodiments set forth herein are taken to be illustrative rather thanlimiting. It should be readily apparent to those of ordinary skill inthe art that various changes and modifications in form and detail may bemade without departing from the spirit and scope of the disclosure.Reference will now be made in detail to the subject matter disclosed,which is illustrated in the accompanying drawings.

Embodiments of the present disclosure are directed to systems andmethods for focus control in extreme ultraviolet lithography systemsusing a focus-sensitive metrology target. Specifically, embodiments ofthe present disclosure are directed to systems and methods ofcontrolling focus of one or more portions of an overlay metrology targetfabrication tool frequently that decrease measurement acquisition timeand that are configurable to permit correction of focus-induced overlaymetrology errors using one or more focus measurements.

A semiconductor device may be formed as multiple printed layers ofpatterned material on a substrate. Each printed layer may be fabricatedthrough a series of process steps such as, but not limited to, one ormore material deposition steps, one or more lithography steps, or one ormore etching steps. During fabrication, each printed layer musttypically be fabricated within selected tolerances to properly constructthe final device. For example, the relative placement of printedelements in each layer (e.g., the overlay or the overlay parameters)must be well characterized and controlled with respect to previouslyfabricated layers. Accordingly, metrology targets may be fabricated onone or more printed layers to enable efficient characterization of theoverlay of the layers. Deviations of focus-sensitive metrology targetfeatures on a printed layer (e.g., pattern placement errors (PPE) in aparticular layer or overlay errors associated with registration errorsbetween sample layers) may thus be representative of deviations ofprinted characteristics of printed device features on that layer.Further, overlay measured at one fabrication step (e.g., after thefabrication of one or more sample layers) may be used to generatecorrectables for precisely aligning a process tool (e.g., a lithographytool, or the like) for the fabrication of an additional sample layer ina subsequent fabrication step.

Focus-sensitive metrology targets typically include featuresspecifically designed to be sensitive to overlay errors between samplelayers of interest. An overlay-type measurement may then be carried outby characterizing the focus-sensitive metrology target using an overlaymetrology tool and applying an algorithm to determine overlay errors onthe sample based on the output of the metrology tool.

Overlay metrology tools may utilize a variety of techniques to determinethe overlay of sample layers. For example, image-based overlay metrologytools may illuminate a focus-sensitive metrology target (e.g., anadvanced imaging metrology (AIM) target, a box-in-box metrology target,or the like) and capture an overlay signal including an image offocus-sensitive metrology target features located on different samplelayers. By way of another example, scatterometry-based overlay metrologytools may illuminate a focus-sensitive metrology target (e.g., agrating-over-grating metrology target, or the like) and capture anoverlay signal including an angular distribution of radiation emanatingfrom the focus-sensitive metrology target associated with diffraction,scattering, and/or reflection of the illumination beam. It is recognizedherein that various overlay metrology tools may be used to measureoverlay. For example, optical metrology tools (e.g., light-basedmetrology tools using electromagnetic radiation for illumination and/ordetection) may provide high-throughput overlay measurements usingnumerous techniques such as, but not limited to, determining relativepositions of spatially-separated features on multiple layers in animage, directly measuring PPE on multiple layers, or scatterometry inwhich overlay is determined based on light scattered and/or diffractedfrom diffraction gratings on multiple layers. For the purposes of thepresent disclosure, the term “optical metrology tools,” “opticalmetrology techniques,” and the like indicate metrology tools andtechniques using electromagnetic radiation of any wavelength such as,but not limited to, x-ray wavelengths, extreme ultraviolet (EUV)wavelengths, vacuum ultraviolet (VUV) wavelengths, deep ultraviolet(DUV) wavelengths, ultraviolet (UV) wavelengths, visible wavelengths, orinfrared (IR) wavelengths. Systems, methods, and apparatuses related tooverlay measurement are generally described in U.S. Pat. No. 8,330,281titled “OVERLAY MARKS, METHODS OF OVERLAY MARK DESIGN AND METHODS OFOVERLAY MEASUREMENTS” and issued on Dec. 11, 2012, U.S. Pat. No.9,476,698 titled “PERIODIC PATTERNS AND TECHNIQUE TO CONTROLMISALIGNMENT BETWEEN TWO LAYERS” and issued on Oct. 25, 2016, U.S. Pat.No. 7,541,201 titled “APPARATUS AND METHODS FOR DETERMINING OVERLAY OFSTRUCTURES HAVING ROTATIONAL OR MIRROR SYMMETRY” and issued on Jun. 2,2009, U.S. Patent Publication No. 2013/0035888 titled “METHOD AND SYSTEMFOR PROVIDING A QUALITY METRIC FOR IMPROVED PROCESS CONTROL” andpublished on Feb. 7, 2013, U.S. Pat. No. 9,214,317 titled “SYSTEM ANDMETHOD OF SEM OVERLAY METROLOGY” and issued on Dec. 15, 2015, U.S. Pat.No. 10,527,951 B2 titled “COMPOUND IMAGING METROLOGY TARGETS” and issuedon Jan. 7, 2020, U.S. Pat. No. 10,190,979 B2 titled “METROLOGY IMAGINGTARGETS HAVING REFLECTION-SYMMETRIC PAIRS OF REFLECTION-ASYMMETRICSTRUCTURES” and issued on Jan. 29, 2019, and PCT Application No.PCT/US2016/039531 titled “APPARATUS AND METHOD FOR THE MEASUREMENT OFPATTERN PLACEMENT AND SIZE OF PATTERN AND COMPUTER PROGRAM THEREFOR” andfiled on Jun. 27, 2016, all of which are incorporated herein byreference in their entirety.

FIG. 1A is a top view of a focus-sensitive metrology target 100, inaccordance with one or more embodiments of the present disclosure. Insome embodiments, one or more portions of the focus-sensitive metrologytarget 100 (e.g., target structures) may be formed on a same layer ofthe focus-sensitive metrology target 100.

The focus-sensitive metrology target 100 may include a first set offirst target structures 102 a and 102 b formed on one or more layers ofa sample (e.g., a current layer and/or a previous layer of the sample).The first set of first target structures 102 a and 102 b may include aplurality of segmented first pattern elements 103 a and 103 b having afirst pitch. The first pitch may be of a value greater than a resolutionof one or more portions of one or more metrology tools configured toperform one or more measurements of one or more portions of thefocus-sensitive metrology target 100 (or another focus-sensitivemetrology target). In this way, the segmented first pattern elements 103a and 103 b may be configured to facilitate the generation of one ormore less-focused images (e.g., when captured by one or more portions ofthe one or more metrology tools).

The plurality of segmented first pattern elements 103 a and 103 b may beconfigured for overlay measurement along at least one measurementdirection (e.g., a y-direction). The plurality of segmented firstpattern elements 103 a and 103 b may be compatible with any metrologymode known in the art to be suitable for the purposes contemplated bythe present disclosure. For example, the one or more first patternelements 103 a and 103 b may be compatible with a diffraction-basedmetrology mode (e.g., a scatterometry-based overlay (SCOL) metrologymode). In this regard, the one or more first pattern elements 103 a and103 b may be configured to include periodic and/or segmented structuresfor metrology using diffraction-based metrology methods (e.g.,grating-over-grating structures, or any structure known in the art to besuitable for diffracting, scattering, and/or reflecting an illuminationbeam). By way of another example, the one or more first pattern elements103 a and 103 b may be compatible with any image-based overlay metrologymode, including, without limitation, an advanced imaging metrology (AIM)mode, a box-in-box metrology mode, or any other metrology mode known inthe art to be suitable for capturing an overlay signal (e.g., an imageof focus-sensitive metrology target features located on different samplelayers).

It is noted that the plurality of segmented first pattern elements 103 aand 103 b may include any one-dimensional or two-dimensional structureformed by any means known in the art, including, without limitation, oneor more lithographic steps, one or more direct etching steps, or thelike. The first set of first target structures 102 a and 102 b and/orthe plurality of segmented first pattern elements 103 a and 103 b may beformed in any shape, including, without limitation, a square shape, around shape, a rhombus-like shape, or a star-like shape.

The focus-sensitive metrology target 100 may include a first set ofsecond target structures 104 a and 104 b formed on one or more layers ofthe sample (e.g., a current layer and/or a previous layer of thesample). The first set of second target structures 104 a and 104 b mayinclude a plurality of segmented second pattern elements 105 a and 105 bhaving a second pitch. The second pitch may be of a value less than theresolution of one or more portions of one or more metrology toolsconfigured to perform one or more measurements of one or more portionsof the focus-sensitive metrology target 100 (or any metrology target).In this way, the segmented second pattern elements 105 a and 105 b maybe configured to facilitate the generation of one or more more-focusedimages (e.g., when captured by one or more portions of the one or moremetrology tools).

The plurality of segmented second pattern elements 105 a and 105 b maybe configured for overlay measurement along at least one measurementdirection (e.g., a y-direction). The plurality of segmented secondpattern elements 105 a and 105 b may be compatible with any metrologymode known in the art to be suitable for the purposes contemplated bythe present disclosure. For example, the one or more second patternelements 105 a and 105 b may be compatible with a diffraction-basedmetrology mode (e.g., a scatterometry-based overlay (SCOL) metrologymode). In this regard, the one or more second pattern elements 105 a and105 b may be configured to include periodic and/or segmented structuresfor metrology using diffraction-based metrology methods (e.g.,grating-over-grating structures, or any structure known in the art to besuitable for diffracting, scattering, and/or reflecting an illuminationbeam). By way of another example, the one or more second patternelements 105 a and 105 b may be compatible with any image-based overlaymetrology mode, including, without limitation, an advanced imagingmetrology (AIM) mode, a box-in-box metrology mode, or any othermetrology mode known in the art to be suitable for capturing an overlaysignal (e.g., an image of focus-sensitive metrology target featureslocated on different sample layers).

It is noted that the plurality of segmented second pattern elements 105a and 105 b may include any one-dimensional or two-dimensional structureformed by any means known in the art, including, without limitation, oneor more lithographic steps, one or more direct etching steps, or thelike. The first set of second target structures 104 a and 104 b and/orthe plurality of segmented second pattern elements 105 a and 105 b maybe formed in any shape, including, without limitation, a square shape, around shape, a rhombus-like shape, or a star-like shape.

In some embodiments, as shown in FIG. 1B, the focus-sensitive metrologytarget 100 may include a first set of third target structures 106 a and106 b formed on one or more layers of the sample (e.g., a current layerand/or a previous layer of the sample). The first set of third targetstructures 106 a and 106 b may include a plurality of segmented thirdpattern elements 107 a and 107 b. The segmented third pattern elements107 a and 107 b may have the first pitch, the second pitch, or a thirdpitch. The third pitch may be equivalent to the first pitch and/or thesecond pitch, or may be different from the first pitch and/or the secondpitch. The third pitch may be configured to facilitate one or moreoverlay measurements between two layers of the sample (e.g., the thirdpitch may be configured such that the third pitch, along with at leastone of the first pitch or the second pitch, may produce one or moreoverlay metrology signals indicative of an overlay error between twosample layers).

It is specifically noted that, in some embodiments, one or more portions(e.g. target structures) of the focus-sensitive metrology target 100 maybe formed on a layer different from a layer on which one or more otherportions of the focus-sensitive metrology target 100 are formed.

The plurality of segmented third pattern elements 107 a and 107 b may beconfigured for overlay measurement along at least one measurementdirection (e.g., a y-direction). The plurality of segmented thirdpattern elements 107 a and 107 b may be compatible with any metrologymode known in the art to be suitable for the purposes contemplated bythe present disclosure. For example, the one or more third patternelements 107 a and 107 b may be compatible with a diffraction-basedmetrology mode (e.g., a scatterometry-based overlay (SCOL) metrologymode). In this regard, the one or more third pattern elements 107 a and107 b may be configured to include periodic and/or segmented structuresfor metrology using diffraction-based metrology methods (e.g.,grating-over-grating structures, or any structure known in the art to besuitable for diffracting, scattering, and/or reflecting an illuminationbeam). By way of another example, the one or more third pattern elements107 a and 107 b may be compatible with any image-based overlay metrologymode, including, without limitation, an advanced imaging metrology (AIM)mode, a box-in-box metrology mode, or any other metrology mode known inthe art to be suitable for capturing an overlay signal (e.g., an imageof focus-sensitive metrology target features located on different samplelayers).

It is noted that the plurality of segmented third pattern elements 107 aand 107 b may include any one-dimensional or two-dimensional structureformed by any means known in the art, including, without limitation, oneor more lithographic steps, one or more direct etching steps, or thelike. The first set of third target structures 106 a and 106 b and/orthe plurality of segmented third pattern elements 107 a and 107 b may beformed in any shape, including, without limitation, a square shape, around shape, a rhombus-like shape, or a star-like shape.

It is specifically noted that the terms “previous layer” and “currentlayer” as used herein are not limited to one previous layer or onecurrent layer. As used herein, the term “previous layer” is intended torefer to one or more layers of the sample formed prior to any otherlayer of the sample designated a “current layer” of the sample. In thisway, the previous layer of the sample may comprise any one or moreprevious layers of the sample formed prior to the current layer of thesample. Similarly, the term “current layer” is intended to refer to oneor more layers of the sample formed after the previous layer of thesample. In this way, the current layer of the sample may comprise anyone or more current layers of the sample formed after the previous layerof the sample.

In some embodiments, as shown in FIG. 1B, the focus-sensitive metrologytarget 100 may include a second set of first target structures 108 a and108 b formed on one or more layers of the sample (e.g., a current layerand/or a previous layer of the sample). The second set of first targetstructures 108 a and 108 b may include a plurality of segmented firstpattern elements 103 c and 103 d having the first pitch, the secondpitch, or the third pitch.

The plurality of segmented first pattern elements 103 c and 103 d may beconfigured for overlay measurement along at least one measurementdirection (e.g., an x-direction). The plurality of segmented firstpattern elements 103 c and 103 d may be compatible with any metrologymode known in the art to be suitable for the purposes contemplated bythe present disclosure. For example, the one or more first patternelements 103 c and 103 d may be compatible with a diffraction-basedmetrology mode (e.g., a scatterometry-based overlay (SCOL) metrologymode). In this regard, the one or more first pattern elements 103 c and103 d may be configured to include periodic and/or segmented structuresfor metrology using diffraction-based metrology methods (e.g.,grating-over-grating structures, or any structure known in the art to besuitable for diffracting, scattering, and/or reflecting an illuminationbeam). By way of another example, the one or more first pattern elements103 c and 103 d may be compatible with any image-based overlay metrologymode, including, without limitation, an advanced imaging metrology (AIM)mode, a box-in-box metrology mode, or any other metrology mode known inthe art to be suitable for capturing an overlay signal (e.g., an imageof focus-sensitive metrology target features located on different samplelayers).

It is noted that the plurality of segmented first pattern elements 103 cand 103 d may include any one-dimensional or two-dimensional structureformed by any means known in the art, including, without limitation, oneor more lithographic steps, one or more direct etching steps, or thelike. The second set of first target structures 108 a and 108 b and/orthe plurality of segmented first pattern elements 103 c and 103 d may beformed in any shape, including, without limitation, a square shape, around shape, a rhombus-like shape, or a star-like shape.

In some embodiments, as shown in FIG. 1B, the focus-sensitive metrologytarget 100 may include a second set of second target structures 110 aand 110 b formed on one or more layers of the sample (e.g., a currentlayer and/or a previous layer of the sample). The second set of secondtarget structures 110 a and 110 b may include a plurality of segmentedsecond pattern elements 105 c and 105 d having the first pitch, thesecond pitch, or the third pitch.

The plurality of segmented second pattern elements 105 c and 105 d maybe configured for overlay measurement along at least one measurementdirection (e.g., an x-direction). The plurality of segmented secondpattern elements 105 c and 105 d may be compatible with any metrologymode known in the art to be suitable for the purposes contemplated bythe present disclosure. For example, the one or more second patternelements 105 c and 105 d may be compatible with a diffraction-basedmetrology mode (e.g., a scatterometry-based overlay (SCOL) metrologymode). In this regard, the one or more second pattern elements 105 c and105 d may be configured to include periodic and/or segmented structuresfor metrology using diffraction-based metrology methods (e.g.,grating-over-grating structures, or any structure known in the art to besuitable for diffracting, scattering, and/or reflecting an illuminationbeam). By way of another example, the one or more second patternelements 105 c and 105 d may be compatible with any image-based overlaymetrology mode, including, without limitation, an advanced imagingmetrology (AIM) mode, a box-in-box metrology mode, or any othermetrology mode known in the art to be suitable for capturing an overlaysignal (e.g., an image of focus-sensitive metrology target featureslocated on different sample layers).

It is noted that the plurality of segmented second pattern elements 105c and 105 d may include any one-dimensional or two-dimensional structureformed by any means known in the art, including, without limitation, oneor more lithographic steps, one or more direct etching steps, or thelike. The second set of second target structures 110 a and 110 b and/orthe plurality of segmented second pattern elements 105 c and 105 d maybe formed in any shape, including, without limitation, a square shape, around shape, a rhombus-like shape, or a star-like shape.

In some embodiments, as shown in FIG. 1B, the focus-sensitive metrologytarget 100 may include a second set of third target structures 112 a and112 b formed on one or more layers of the sample (e.g., a current layerand/or a previous layer of the sample). The second set of third targetstructures 112 a and 112 b may include a plurality of segmented thirdpattern elements 107 c and 107 d having the first pitch, the secondpitch, or the third pitch.

The plurality of segmented third pattern elements 107 c and 107 d may beconfigured for overlay measurement along at least one measurementdirection (e.g., an x-direction). The plurality of segmented thirdpattern elements 107 c and 107 d may be compatible with any metrologymode known in the art to be suitable for the purposes contemplated bythe present disclosure. For example, the one or more third patternelements 107 c and 107 d may be compatible with a diffraction-basedmetrology mode (e.g., a scatterometry-based overlay (SCOL) metrologymode). In this regard, the one or more third pattern elements 107 c and107 d may be configured to include periodic and/or segmented structuresfor metrology using diffraction-based metrology methods (e.g.,grating-over-grating structures, or any structure known in the art to besuitable for diffracting, scattering, and/or reflecting an illuminationbeam). By way of another example, the one or more third pattern elements107 c and 107 d may be compatible with any image-based overlay metrologymode, including, without limitation, an advanced imaging metrology (AIM)mode, a box-in-box metrology mode, or any other metrology mode known inthe art to be suitable for capturing an overlay signal (e.g., an imageof focus-sensitive metrology target features located on different samplelayers).

It is noted that the plurality of segmented third pattern elements 107 cand 107 d may include any one-dimensional or two-dimensional structureformed by any means known in the art, including, without limitation, oneor more lithographic steps, one or more direct etching steps, or thelike. The second set of third target structures 112 a and 112 b and/orthe plurality of segmented third pattern elements 107 c and 107 d may beformed in any shape, including, without limitation, a square shape, around shape, a rhombus-like shape, or a star-like shape.

In some embodiments, as shown in FIG. 1B, the first set of first targetstructures 102 a and 102 b may be rotationally symmetric to the secondset of first target structures 108 a and 108 b about a center ofsymmetry 114. For example, the first set of first target structures 102a and 102 b may be four-fold rotationally symmetric to the second set offirst target structures 108 a and 108 b about the center of symmetry114.

In some embodiments, as shown in FIG. 1B, the first set of second targetstructures 104 a and 104 b may be rotationally symmetric to the secondset of second target structures 110 a and 110 b about the center ofsymmetry 114. For example, the first set of second target structures 104a and 104 b may be four-fold rotationally symmetric to the second set ofsecond target structures 110 a and 110 b about the center of symmetry114.

In some embodiments, as shown in FIG. 1B, the first set of third targetstructures 106 a and 106 b may be rotationally symmetric to the secondset of third target structures 112 a and 112 b about the center ofsymmetry 114. For example, the first set of third target structures 106a and 106 b may be four-fold rotationally symmetric to the second set ofthird target structures 112 a and 112 b about the center of symmetry114.

It is noted that the embodiments of the present disclosure are notlimited to those embodiments including rotational symmetry. For example,with respect to two or more layers of the sample, the embodiments of thepresent disclosure may not display rotational symmetry when an overlayerror exists between the two or more layers.

It is contemplated that the focus-sensitive metrology target 100 is notlimited to embodiments having a second set of first target structures108 a and 108 b, a second set of second target structures 110 a and 110b, and/or a second set of third target structures 112 a and 112 b. Forexample, in some embodiments, as shown in FIG. 1A, the focus-sensitivemetrology target 100 may include only the first set of first targetstructures 102 a and 102 b, and the first set of second targetstructures 104 a and 104 b.

In some embodiments, as shown in FIG. 1C, the plurality of segmentedfirst pattern elements 103 a and 103 b and the plurality of segmentedsecond pattern elements 105 a and 105 b may be configured to increasefocus and/or metrology measurement sensitivity and to include a greaterfocus response than other metrology targets (e.g., single layermetrology targets). For example, the plurality of segmented firstpattern elements 103 a and 103 b and the plurality of segmented secondpattern elements 105 a and 105 b may each include a Moiré pattern formedalong a direction (e.g., a y-direction) from overlapping periodicstructures formed on different layers of the sample. By way of anotherexample, each of the plurality of segmented first pattern elements 103 aand 103 b and the plurality of segmented second pattern elements 105 aand 105 b may include two or more overlapping periodic structures, whereeach of the overlapping periodic structures is formed on a differentlayer of the sample. The periodicity of each the overlapping periodicstructures may be of a period (e.g., a distance of separation betweenrepeated elements of the overlapping periodic structure) betweenapproximately 300 nanometers and approximately 700 nanometers, and theperiod of each of the overlapping periodic structures may be of adifferent value within the range of approximately 300 nanometers andapproximately 700 nanometers. For example, one overlapping periodicstructure may have a period of approximately 420 nanometers, whileanother overlapping periodic structure may have a period ofapproximately 480 nanometers. In this way, the overlapping periodicstructures may be configured to produce a Moiré effect when illuminatedand/or imaged in such a way that measurement accuracy (e.g., metrologymeasurement and/or focus measurement) is increased. By way of anotherexample, the overlapping periodic structures may be configured toproduce a Moiré grating-over-grating effect, such as a double scatteringMoiré effect (e.g., collecting 0-order diffraction and at least oneMoiré diffraction order), or a method of measuring overlay using asingle scattering optical Moiré effect (a Moiré effect that appears on acamera due to the interference between single scattering effects, e.g.,collecting 1st-order diffraction and filtering an image to isolate Moiréinterference). The use of Moiré patterns in overlay metrology isgenerally described in U.S. Pat. No. 7,440,105, issued on Oct. 21, 2008,U.S. Pat. No. 7,349,105, issued on Mar. 25, 2008, and U.S. Patent App.Publ. No. 2018/0188663, published on Jul. 5, 2018, each of which isincorporated herein in the entirety. It is noted that the embodiments ofthe present disclosure are not limited to the plurality of segmentedfirst pattern elements 103 a and 103 b and the plurality of segmentedsecond pattern elements 105 a and 105 b having a Moiré pattern. Forexample, the plurality of segmented third pattern elements 107 a and 107b may include a Moiré pattern.

In some embodiments, as shown in FIG. 1D, the focus-sensitive metrologytarget 100 may include a first set of fourth target structures 115 a and115 b formed on one or more layers of the sample (e.g., a current layerand/or a previous layer of the sample). The first set of fourth targetstructures 115 a and 115 b may include a plurality of segmented fourthpattern elements 116 a and 116 b having a Moiré pattern.

The plurality of segmented fourth pattern elements 116 a and 116 b maybe configured for overlay measurement along at least one measurementdirection (e.g., a y-direction). The plurality of segmented fourthpattern elements 116 a and 116 b may be compatible with any metrologymode known in the art to be suitable for the purposes contemplated bythe present disclosure. For example, the one or more fourth patternelements 116 a and 116 b may be compatible with a diffraction-basedmetrology mode (e.g., a scatterometry-based overlay (SCOL) metrologymode). In this regard, the one or more fourth pattern elements 116 a and116 b may be configured to include periodic and/or segmented structuresfor metrology using diffraction-based metrology methods (e.g.,grating-over-grating structures, or any structure known in the art to besuitable for diffracting, scattering, and/or reflecting an illuminationbeam). By way of another example, the one or more fourth patternelements 116 a and 116 b may be compatible with any image-based overlaymetrology mode, including, without limitation, an advanced imagingmetrology (AIM) mode, a box-in-box metrology mode, or any othermetrology mode known in the art to be suitable for capturing an overlaysignal (e.g., an image of focus-sensitive metrology target 100 featureslocated on different sample layers).

It is noted that the plurality of segmented fourth pattern elements 116a and 116 b may include any one-dimensional or two-dimensional structureformed by any means known in the art, including, without limitation, oneor more lithographic steps, one or more direct etching steps, or thelike. The first set of fourth target structures 115 a and 115 b and/orthe plurality of segmented fourth pattern elements 116 a and 116 b maybe formed in any shape, including, without limitation, a square shape, around shape, a rhombus-like shape, or a star-like shape.

It is further noted that the first set of fourth target structures 115 aand 115 b may allow the focus-sensitive metrology target 100 to be usedfor more accurate overlay metrology measurements. For example, theinclusion of the first set of fourth target structures 115 a and 115 bwith the first set of first target structures 102 a and 102 b, the firstset of second target structures 104 a and 104 b, and/or the first set ofthird target structures 106 a and 106 b may allow for additionalmetrology measurements based on one or more signals emanating from thefirst set of first target structures 102 a and 102 b, the first set ofsecond target structures 104 a and 104 b, the first set of third targetstructures 106 a, and/or the first set of fourth target structures 115 aand 115 b.

FIG. 2 illustrates a simplified block diagram of a focus control system200, in accordance with one or more embodiments of the presentdisclosure. In one embodiment, the focus control system 200 includes oneor more fabrication tools 210. The one or more fabrication tools 210 mayinclude any tool configured to form an overlay metrology target,including, without limitation, any lithographic tool, any EUV scanner,or the like.

In some embodiments, the focus control system 200 includes one or moremetrology tools 202. The one or more metrology tools 202 may beconfigured to operate in either an imaging mode or a non-imaging mode.For example, in an imaging mode, individual focus-sensitive metrologytarget 100 elements may be resolvable within the illuminated spot on thesample (e.g., as part of a bright-field image, a dark-field image, aphase-contrast image, or the like). By way of another example, the oneor more metrology tools 202 may operate as a scatterometry-based overlay(SCOL) metrology tool in which radiation from the sample is analyzed ata pupil plane to characterize the angular distribution of radiation fromthe sample (e.g., associated with scattering and/or diffraction ofradiation by the sample).

The one or more metrology tools 202 may direct illumination to a sampleand may further collect radiation emanating from the sample to generatean overlay signal suitable for the determination of overlay of two ormore sample layers. The one or more metrology tools 202 may include anytype of overlay metrology tool known in the art suitable for generatingoverlay signals suitable for determining overlay associated withmetrology targets on a sample, including, without limitation, anyoptical metrology tool (e.g., an advanced imaging metrology (AIM) tool,an advanced imaging metrology in-die (AIMid) tool, a triple advancedimaging metrology (Triple AIM) tool, Archer, and the like), anyparticle-based metrology tool (e.g., an electron-beam metrology tool),or a scatterometry-based overlay (SCOL) metrology tool.

The one or more metrology tools 202 may be configurable to generateoverlay signals based on any number of recipes defining measurementparameters for acquiring an overlay signal suitable for determiningoverlay of a focus-sensitive metrology target 100. For example, a recipeof the one or more metrology tools 202 may include, but is not limitedto, an illumination wavelength, a detected wavelength of radiationemanating from the sample, a spot size of illumination on the sample, anangle of incident illumination, a polarization of incident illumination,wave plan of the incident beam, a position of a beam of incidentillumination on an focus-sensitive metrology target, a position of anfocus-sensitive metrology target in the focal volume of the overlaymetrology tool, or the like.

In another embodiment, the focus control system 200 includes acontroller 204 communicatively coupled to the one or more fabricationtools 210 and/or the one or more metrology tools 202. The controller 204may be configured to direct the one or more fabrication tools 210 toperform one or more steps in the fabrication of a focus-sensitivemetrology target 100. The controller 204 may be configured to direct theone or more metrology tools 202 to generate overlay signals based on oneor more selected recipes. The controller 204 may be further configuredto receive data including, but not limited to, overlay signals (e.g.,signals indicative of illumination emanating from one or morefocus-sensitive metrology targets) from the one or more metrology tools202. Additionally, the controller 204 may be configured to determine oneor more focus-offset values based on the one or more signals indicativeof illumination emanating from the one or more focus-sensitive metrologytargets 100. In some embodiments, the controller 204 may be configuredto determine overlay associated with a focus-sensitive metrology target100 based on the acquired overlay signals.

In another embodiment, the controller 204 includes one or moreprocessors 206. For example, the one or more processors 206 may beconfigured to execute a set of program instructions maintained in amemory medium 208, or memory. The controller 204 may be configured todetermine an overlay error of a sample having one or morefocus-sensitive metrology targets 100 based on one or more overlaymeasurements of the sample. For example, in one embodiment, themetrology sub-system 202 may direct illumination to a sample having oneor more focus-sensitive metrology targets 100. In another embodiment,the metrology sub-system 202 may be configured to further collectradiation emanating from the sample to generate one or more overlaymeasurements (or one or more signals indicative of one or more overlaymeasurements) suitable for the determination of overlay of two or moresample layers. In another embodiment, the controller 204 may beconfigured to determine one or more focus-offset values based on the oneor more signals indicative of illumination emanating from the sample.

In one embodiment, the controller 204 may be configured to determine oneor more focus-offset values of the sample based on signals indicative ofillumination emanating from the first set of first target structures 102a and 102 b, the second set of first target structures 108 a and 108 b,the first set of second target structures 104 a and 104 b, the secondset of second target structures 110 a and 110 b, the first set of thirdtarget structures 106 a and 106 b, the second set of third targetstructures 112 a and 112 b, and/or the first set of fourth targetstructures 115 a and 115 b. For example, the controller 204 may beconfigured to generate one or more focus off-set values by comparing thesignals indicative of illumination emanating from the first set of firsttarget structures 102 a and 102 b, the second set of first targetstructures 108 a and 108 b, the first set of second target structures104 a and 104 b, the second set of second target structures 110 a and110 b, the first set of third target structures 106 a and 106 b, thesecond set of third target structures 112 a and 112 b, and/or the firstset of fourth target structures 115 a and 115 b to a pre-determinedcalibration function stored in memory 208. The pre-determinedcalibration function maybe constructed either through simulation or by adedicated focus-sensitivity experiment. By way of another example, thepre-determined calibration function may be generated by performing aplurality of measurements at varying but known levels of focus. As anadditional example, the pre-determined calibration function may includeany simulation and/or function that may predict an actual focus ofapproximately one nanometer over a focus range, including, withoutlimitation, one or more Prolith simulations. In another embodiment, thecontroller 204 may be configured to determine one or more focus-offsetvalues of the sample based on signals indicative of illuminationemanating from the first set of first target structures 102 a and 102 b,the second set of first target structures 108 a and 108 b, the first setof second target structures 104 a and 104 b, the second set of secondtarget structures 110 a and 110 b, the first set of third targetstructures 106 a and 106 b, the second set of third target structures112 a and 112 b, and/or the first set of fourth target structures 115 aand 115 b. For example, the controller 204 may be configured to generateone or more focus off-set values by comparing the signals indicative ofillumination emanating from the first set of first target structures 102a and 102 b, the second set of first target structures 108 a and 108 b,the first set of second target structures 104 a and 104 b, the secondset of second target structures 110 a and 110 b, the first set of thirdtarget structures 106 a and 106 b, the second set of third targetstructures 112 a and 112 b, and/or the first set of fourth targetstructures 115 a and 115 b to a pre-determined calibration functionstored in memory 208.

In another embodiment, the controller 204 may be configured to determinean overlay error of a sample having one or more focus-sensitivemetrology targets 100 based on one or more overlay measurements of thesample. For example, the controller 204 may be configured to generateone or more overlay measurements of the sample based on one or moresignals indicative of illumination emanating from one or more portionsof the sample (e.g., the first set of first target structures 102 a and102 b, the second set of first target structures 108 a and 108 b, thefirst set of second target structures 104 a and 104 b, the second set ofsecond target structures 110 a and 110 b, the first set of third targetstructures 106 a and 106 b, the second set of third target structures112 a and 112 b, and/or the first set of fourth target structures 115 aand 115 b). The one or more overlay measurements of the sample maycorrespond to an overlay position of one or more layers of the sample.The controller 204 may be configured to generate one or more correctedoverlay measurements by correcting one or more uncorrected overlaymeasurements (e.g., overlay measurements taken without regard to properand/or desired focus) using the one or more focus-offset values. In thisregard, the controller 204 may be configured to provide one or morefocus corrections determined based on the one or more focus-offsetvalues to one or more portions of the one or more metrology tools 202.

It is noted herein that the embodiments of the present disclosure,including, without limitation, those embodiments of the focus-sensitivemetrology target 100 configured for focus correction and overlaymetrology, are configured to increase the efficiency of overlaymetrology measurements and to decrease measurement cycle time. Forexample, in some embodiments, the focus-sensitive metrology target 100may be configured to simultaneously (or nearly-simultaneously) correct afocus of one or more components of the one or more portions of the focuscontrol system 200 and generate one or more metrology measurements at adesired focus.

The one or more processors 206 of the controller 204 may include anyprocessor or processing element known in the art. For the purposes ofthe present disclosure, the term “processor” or “processing element” maybe broadly defined to encompass any device having one or more processingor logic elements (e.g., one or more micro-processor devices, one ormore application specific integrated circuit (ASIC) devices, one or morefield programmable gate arrays (FPGAs), or one or more digital signalprocessors (DSPs)). In this sense, the one or more processors 206 mayinclude any device configured to execute algorithms and/or instructions(e.g., program instructions stored in memory 208). In one embodiment,the one or more processors 206 may be embodied as a desktop computer,mainframe computer system, workstation, image computer, parallelprocessor, networked computer, or any other computer system configuredto execute a program configured to operate or operate in conjunctionwith the metrology system 300, as described throughout the presentdisclosure. Further, the steps described throughout the presentdisclosure may be carried out by a single controller 204 or,alternatively, multiple controllers. Additionally, the controller 204may include one or more controllers housed in a common housing or withinmultiple housings. In this way, any controller or combination ofcontrollers may be separately packaged as a module suitable forintegration into metrology system 300. Further, the controller 204 mayanalyze data received from the one or more metrology tools 202 and/orthe one or more fabrication tools 210 and feed the data to additionalcomponents within the focus control system 200 or external to the focuscontrol system 200.

The memory medium 208 may include any storage medium known in the artsuitable for storing program instructions executable by the associatedone or more processors 206. For example, the memory medium 208 mayinclude a non-transitory memory medium. By way of another example, thememory medium 208 may include, but is not limited to, a read-only memory(ROM), a random-access memory (RAM), a magnetic or optical memory device(e.g., disk), a magnetic tape, a solid-state drive and the like. It isfurther noted that memory medium 208 may be housed in a commoncontroller housing with the one or more processors 206. In oneembodiment, the memory medium 208 may be located remotely with respectto the physical location of the one or more processors 206 andcontroller 204. For instance, the one or more processors 206 of thecontroller 204 may access a remote memory (e.g., server), accessiblethrough a network (e.g., internet, intranet and the like).

In one embodiment, a user interface (not shown) may be communicativelycoupled to the controller 204. The user interface may include, but isnot limited to, one or more desktops, laptops, tablets, and the like. Inanother embodiment, the user interface includes a display used todisplay data of the focus control system 200 to a user. The display ofthe user interface may include any display known in the art. Forexample, the display may include, but is not limited to, a liquidcrystal display (LCD), an organic light-emitting diode (OLED) baseddisplay, or a CRT display. Those skilled in the art should recognizethat any display device capable of integration with a user interface issuitable for implementation in the present disclosure. In anotherembodiment, a user may input selections and/or instructions responsiveto data displayed to the user via a user input device of the userinterface.

In one embodiment, as shown in FIG. 3, the focus control system 200 mayinclude one or more metrology tools 202. In some embodiments, the one ormore metrology tools 202 may include an optical metrology tool,including, without limitation, an optical metrology tool configured togenerate and/or detect an optical illumination beam having x-ray,ultraviolet (UV), infrared (IR), or visible light wavelengths. By way ofanother example, the one or more metrology tools 202 may include anadvanced imaging metrology (AIM) tool, an advanced imaging metrologyin-die (AIMid) tool, or a triple advanced imaging metrology (Triple AIM)tool.

In one embodiment, the one or more metrology tools 202 may include anoptical illumination source 302 configured to generate an opticalillumination beam 304. The optical illumination beam 304 may include oneor more selected wavelengths of radiation including, but not limited to,x-ray, ultraviolet (UV) light, visible light, or infrared (IR) light.

The optical illumination source 302 may include any type of illuminationsource suitable for providing an optical illumination beam 304. In oneembodiment, the optical illumination source 302 is a laser source. Forexample, the optical illumination source 302 may include, but is notlimited to, one or more narrowband laser sources, a broadband lasersource, a supercontinuum laser source, a white light laser source, orthe like. In this regard, the optical illumination source 302 mayprovide an optical illumination beam 304 having high coherence (e.g.,high spatial coherence and/or temporal coherence). In anotherembodiment, the optical illumination source 302 includes alaser-sustained plasma (LSP) source. For example, the opticalillumination source 302 may include, but is not limited to, a LSP lamp,a LSP bulb, or a LSP chamber suitable for containing one or moreelements that, when excited by a laser source into a plasma state, mayemit broadband illumination. In another embodiment, the opticalillumination source 302 includes a lamp source. For example, the opticalillumination source 302 may include, but is not limited to, an arc lamp,a discharge lamp, an electrode-less lamp, or the like. In this regard,the optical illumination source 302 may provide an optical illuminationbeam 304 having low coherence (e.g., low spatial coherence and/ortemporal coherence).

In another embodiment, the optical illumination source 302 directs theoptical illumination beam 304 to the sample 320 via an illuminationpathway 310. The illumination pathway 310 may include one or moreillumination pathway lenses 308 or additional optical components 306suitable for modifying and/or conditioning the optical illumination beam304. For example, the one or more optical components 306 may include,but are not limited to, one or more polarizers, one or more filters, oneor more beam splitters, one or more diffusers, one or more homogenizers,one or more apodizers, or one or more beam shapers. The illuminationpathway 310 may further include an objective lens 316 configured todirect the optical illumination beam 304 to the sample 320.

In another embodiment, the sample 320 is disposed on a sample stage 322.The sample stage 322 may include any device suitable for positioningand/or scanning the sample 320 within the one or more metrology tools202. For example, the sample stage 322 may include any combination oflinear translation stages, rotational stages, tip/tilt stages, or thelike.

In another embodiment, the one or more metrology tools 202 include oneor more detectors 324 configured to capture light emanating from thesample 320 through a collection pathway 314. The collection pathway 314may include, but is not limited to, one or more collection pathwaylenses 312, 318 for collecting light from the sample 320. For example,the one or more detectors 324 may receive light reflected or scattered(e.g., via specular reflection, diffuse reflection, and the like) fromthe sample 320 via one or more collection pathway lenses 312, 318. Byway of another example, the one or more detectors 324 may receive lightgenerated by the sample 320 (e.g., luminescence associated withabsorption of the optical illumination beam 304, or the like). By way ofanother example, the one or more detectors 324 may receive one or morediffracted orders of light from the sample 320 (e.g., 0-orderdiffraction, ±1 order diffraction, ±2 order diffraction, and the like).

The one or more detectors 324 may include any type of detector known inthe art suitable for measuring illumination received from the sample320. For example, a detector 324 may include, but is not limited to, aCCD detector, a TDI detector, a photomultiplier tube (PMT), an avalanchephotodiode (APD), a complementary metal-oxide-semiconductor (CMOS)sensor, or the like. In another embodiment, a detector 324 may include aspectroscopic detector suitable for identifying wavelengths of lightemanating from the sample 320.

In one embodiment, the one or more detectors 324 are positionedapproximately normal to the surface of the sample 320. In anotherembodiment, the one or more metrology tools 202 includes a beamsplitteroriented such that the objective lens 316 may simultaneously direct theoptical illumination beam 304 to the sample 320 and collect lightemanating from the sample 320. Further, the illumination pathway 310 andthe collection pathway 314 may share one or more additional elements(e.g., objective lens 316, apertures, filters, or the like).

It is to be understood that the description of the one or more metrologytools 202, as depicted in FIG. 3, and the associated descriptions above,are provided solely for illustrative purposes and should not beinterpreted as limiting. For example, the one or more metrology tools202 may include a multi-beam and/or a multi-column system suitable forsimultaneously interrogating a sample 320. In a further embodiment, oneor more metrology tools 202 may include one or more components (e.g.,one or more electrodes) configured to apply one or more voltages to oneor more locations of the sample 320. In this regard, the one or moremetrology tools 202 may generate voltage contrast imaging data.

As previously described, the focus control system 200 may include acontroller 204 communicatively coupled to the one or more metrologytools 202 and/or the one or more fabrication tools 210. The controller204 may be configured to direct the one or more metrology tools 202 togenerate overlay signals based on one or more selected recipes. Thecontroller 204 may be further configured to receive data including, butnot limited to, overlay signals from the one or more metrology tools 202and/or the one or more fabrication tools 210. Additionally, thecontroller 204 may be configured to determine overlay associated with afocus-sensitive metrology target 100 based on the acquired overlaysignals. For example, the controller 204 may be configured to generateone or more overlay measurements of the sample based on one or moresignals indicative of illumination emanating from one or more portionsof the sample (e.g., the first set of first target structures 102 a and102 b, the second set of first target structures 108 a and 108 b, thefirst set of second target structures 104 a and 104 b, the second set ofsecond target structures 110 a and 110 b, the first set of third targetstructures 106 a and 106 b, the second set of third target structures112 a and 112 b, and/or the first set of fourth target structures 115 aand 115 b). The one or more overlay measurements of the sample maycorrespond to an overlay position of one or more layers of the sample.The controller 204 may be configured to generate one or more correctedoverlay measurements by correcting one or more uncorrected overlaymeasurements (e.g., overlay measurements taken without regard to properand/or desired focus) using the one or more focus-offset values. In thisregard, the controller 204 may be configured to provide one or morefocus corrections determined based on the one or more focus-offsetvalues to one or more portions of the focus control system 200.

FIG. 4 illustrates a process flow diagram depicting the steps of amethod 400 of focus control, in accordance with one or more embodimentsof the present disclosure.

In Step 402, one or more signals indicative of illumination emanatingfrom one or more focus-sensitive metrology targets 100 of a sample arereceived. For example, a sample including one or more focus-sensitivemetrology targets 100 may be illuminated with an illumination beam, anda reflected beam may emanate from the one or more metrology targets 100and may be detected by one or more portions of the focus control system200. As used herein, the term “illumination beam” may refer to anyradiant beam, including, without limitation, the illumination beam 304,and the term “reflected beam” may refer to any reflected beam 308.

In Step 404, one or more focus-offset values are determined based on theone or more signals indicative of illumination emanating from the one ormore focus-sensitive metrology targets 100. For example, the controller204 may be configured to determine one or more focus-offset values ofthe sample based on signals indicative of illumination emanating fromthe first set of first target structures 102 a and 102 b, the second setof first target structures 108 a and 108 b, the first set of secondtarget structures 104 a and 104 b, the second set of second targetstructures 110 a and 110 b, the first set of third target structures 106a and 106 b, the second set of third target structures 112 a and 112 b,and/or the first set of fourth target structures 115 a and 115 b. By wayof another example, the controller 204 may be configured to generate oneor more focus off-set values by comparing the signals indicative ofillumination emanating from the first set of first target structures 102a and 102 b, the second set of first target structures 108 a and 108 b,the first set of second target structures 104 a and 104 b, the secondset of second target structures 110 a and 110 b, the first set of thirdtarget structures 106 a and 106 b, the second set of third targetstructures 112 a and 112 b, and/or the first set of fourth targetstructures 115 a and 115 b, to a pre-determined calibration functionstored in memory 208. The pre-determined calibration function maybeconstructed either through simulation or by a dedicatedfocus-sensitivity experiment. For example, the pre-determinedcalibration function may be generated by performing a plurality ofmetrology measurements at varying but known levels of focus. In anotherembodiment, the controller 204 may be configured to determine one ormore focus-offset values of the sample based on signals indicative ofillumination emanating from the first set of first target structures 102a and 102 b, the second set of first target structures 108 a and 108 b,the first set of second target structures 104 a and 104 b, the secondset of second target structures 110 a and 110 b, the first set of thirdtarget structures 106 a and 106 b, the second set of third targetstructures 112 a and 112 b, and/or the first set of fourth targetstructures 115 a and 115 b.

In Step 406, one or more focus corrections are provided based on the oneor more focus-offsets determined in at least Step 404. For example, Step406 may include the controller 204 generating one or more controlsignals (or corrections to the control signals) for adjusting one ormore parameters (e.g., fabrication settings, configuration, and thelike) of one or more fabrication tools 210 (e.g., lithographic tools,EUV scanner, or the like). The control signals (or corrections to thecontrol signals) may be provided by the controller 204 as part of afeedback and/or feedforward control loop. The controller 204 may causethe one or more fabrication tools 210 to execute one or more adjustmentsto the one or more parameters of the one or more process tools based onthe one or more control signals (or corrections to the control signals).In some embodiments, the controller 204 may alert a user to make the oneor more adjustments. In this sense, the one or more control signals maycompensate for errors of one or more fabrication processes of the one ormore fabrication tools 210, and thus may enable the one or morefabrication tools 210 to maintain overlay within selected tolerancesacross multiple exposures on subsequent samples in the same or differentlots.

FIG. 5 illustrates a process flow diagram depicting the steps of amethod 500 of selecting one or more metrology target designs as part ofa focus control method, in accordance with one or more embodiments ofthe present disclosure. It is noted that any one or more of the steps ofmethod 500, or the method 500 as a whole, may be performed as one ormore sub-steps of any step of any of the methods disclosed herein,including, without limitation, as one or more sub-steps of the method400.

In Step 502, one or more fabrication simulations are performed under oneor more simulated illumination conditions. For example, the one or morefabrication simulations (e.g., lithography simulations) may include oneor more Prolith simulations. The one or more simulated illuminationconditions may include conditions that may correspond and/or contributeto the existence of one or more biases (e.g., critical dimension bias)with respect to the fabrication of one or more portions of one or moremetrology targets (e.g., outer lines, spaces, patterns, or the like)fabricated on a sample. For example, the one or more simulatedillumination conditions may include variations in a quantity of lines,spaces, and/or segments of one or more patterns typically fabricated onthe sample. It is noted that the one or more fabrication simulations maybe carried out in a virtual space, and that the one or more fabricationsimulations may be configured to produce results indicative of resultsthat would be expected in a real-world fabrication context. In someembodiments, the one or more fabrication simulations may be carried outusing a simulated, simplified metrology target. For example, the one ormore fabrication simulations may be carried out using a simulatedmetrology target that contains fewer features (e.g., a segmented coarsebar having relatively small dimensions) but that is representative of agiven metrology target of interest (e.g., that contains a pitchrepresentative of a metrology target of interest). It is noted that useof the simulated, simplified metrology target may serve to decrease theamount of time required to perform the one or more fabricationsimulations.

In Step 504, one or more fabrication biases are determined based on theone or more fabrication simulations. For example, the one or morefabrication simulations may be performed such that one or more simulatedbiases and/or pattern placement errors may be determined. In thisregard, the one or more fabrication simulations may be predictive offabrication errors that may occur during a fabrication process of aparticular metrology target of interest.

In Step 506, one or more metrology target design simulations areperformed under one or more simulated focus conditions. For example, oneor more simulations may be performed using one or more selectedmetrology target designs of interest. By way of another example, the oneor more metrology target design simulations may be performed using oneor more metrology target designs having wafer stack designs similar to aselected metrology target design of interest. The one or more metrologytarget design simulations may be performed under one or more simulatedfocus conditions. For example, the one or more simulated focusconditions may include illumination settings of one or more metrologytools, such as wavelength, polarization, or bandwidth. It is noted thatthe one or more metrology target design simulations may be carried outin a virtual space, and that the one or more metrology target designsimulations may be configured to produce results indicative of resultsthat would be expected in a real-world metrology context.

In Step 508, one or more focus-sensitive metrology parameters aredetermined based on the one or more metrology target design simulations.For example, the effect of varying metrology target designs (e.g.,segmentation pitch) on one or more aspects of focus measurement and/oroverlay metrology may be determined.

In Step 510, one or more metrology target designs having one or morefocus-sensitive metrology parameters are selected. For example, one ormore metrology target designs having a desired focus-sensitivityparameter (e.g., through-focus response) may be selected. By way ofanother example, a metrology target design having target features formedon a plurality of layers of the sample, where one or morefocus-sensitivity parameters (e.g., a relative difference in thethrough-focus response of the target features formed on a plurality oflayers of the sample) are desired, may be selected.

FIG. 6 illustrates a process flow diagram depicting the steps of amethod 600 determining one or more focus errors as part of a focuscontrol method, in accordance with one or more embodiments of thepresent disclosure. It is noted that any one or more of the steps ofmethod 600, or the method 600 as a whole, may be performed as one ormore sub-steps of any step of any of the methods disclosed herein,including, without limitation, as one or more sub-steps of the method400.

In Step 602, a plurality of calibration simulations based on one or moreselected metrology target designs may be performed. For example, aplurality of fabrication simulations and/or a plurality of metrologytarget design simulations may be performed on a selected metrologytarget design (e.g., a metrology target design of interest and for whichfocus errors will be determined) such that a plurality of fabricationbiases and/or a plurality of focus parameters for varying illuminationconditions and/or focus conditions may be determined for the selectedmetrology target design.

In Step 604, one or more calibration curves may be generated based onthe plurality of calibration simulations. For example, one or morecalibration curves may be generated, where one or more valuescorresponding to the illumination conditions and/or focus conditions maybe plotted against one or more values corresponding to a range offabrication biases and/or focus parameters. In this regard, the one ormore calibration curves may be used to determine a focus error resultingfrom at least one of the illumination conditions or the focus conditionsby comparing one or more overlay measurements generated based on theselected metrology target design (such as the overlay measurementsgenerated in method 700 described herein) to the one or more calibrationcurves.

In Step 606, one or more focus errors are determined by comparing one ormore overlay measurements of a sample having one or more metrologytarget designs corresponding to the one or more selected targetmetrology designs. For example, the one or more overlay measurements ofthe sample may be compared to the one or more calibration curves, basedon one or more illumination conditions and/or focus conditions existingduring the generation of the one or more overlay measurements. In thisregard, the one or more overlay measurements may be translated to one ormore signals indicative of one or more focus errors that may existwithin a fabrication process. In some embodiments, one or more focuscorrections may be provided based on the one or more focus errors. Forexample, one or more control signals (or corrections to the controlsignals) may be generated to adjust one or more parameters (e.g.,fabrication conditions, illumination conditions, fabrication toolconfiguration, and the like) of one or more fabrication tools 210 (e.g.,lithographic tools, EUV scanner, or the like). The control signals (orcorrections to the control signals) may be provided (e.g., by thecontroller 204) as part of a feedback and/or feedforward control loop.The controller 204 may cause the one or more process tools to executeone or more adjustments to the one or more parameters of the one or morefabrication tools based on the one or more control signals (orcorrections to the control signals). In some embodiments, the controller204 may alert a user to make the one or more adjustments. In this sense,the one or more control signals may compensate for errors of one or morefabrication processes of the one or more process tools, and thus mayenable the one or more process tools to maintain overlay within selectedtolerances across multiple exposures on subsequent samples in the sameor different lots.

It is noted that, in some embodiments, one or more focus errors may bedetermined in Step 606 by generating a machine learning classifier andproviding one or more overlay measurements to the machine learningclassifier, where the machine learning classifier is configured todetermine one or more focus errors. The machine learning classifier mayinclude any type of machine learning algorithm/classifier and/or deeplearning technique or classifier known in the art including, but notlimited to, a random forest classifier, a support vector machine (SVM)classifier, an ensemble learning classifier, an artificial neuralnetwork (ANN), and the like. By way of another example, the machinelearning classifier may include a deep convolutional neural network(CNN). For instance, in some embodiments, the machine learningclassifier may include ALEXNET and/or GOOGLENET. In this regard, themachine learning classifier may include any algorithm, classifier, orpredictive model configured to determine one or more focus errors.

It is further noted that the one or more fabrication simulations and theone or more calibration simulations may be performed on varyingillumination and/or focus conditions. For example, the one or morefabrication simulations and the one or more calibration simulations maybe performed using illumination and/or focus conditions that maycorrespond to a variation in one or more process tools of the system 200(e.g., the fabrication tool 210), including, without limitation,deviations with respect to the one or more process tools (e.g., driftthat occurs as the one or more process tools become aged).

FIG. 7 illustrates a process flow diagram depicting the steps of amethod 700 of measuring overlay of a sample, in accordance with one ormore embodiments of the present disclosure.

In Step 702, a sample including one or more focus-sensitive metrologytargets 100 is illuminated. For example, the one or more metrology tools202 may direct an illumination beam onto the sample. As used herein, theterm “illumination beam” may refer to any radiant beam, including,without limitation, the optical illumination beam 304.

In Step 704, illumination emanating from the one or more focus-sensitivemetrology targets 100 is detected. For example, the optical illuminationbeam 304 may be detected. By way of another example, the one or moremetrology tools 202 may be configured to detect illumination emanatingfrom one or more portions of the one or more focus-sensitive metrologytargets 100 (e.g., the first set of first target structures 102 a and102 b, the second set of first target structures 108 a and 108 b, thefirst set of second target structures 104 a and 104 b, the second set ofsecond target structures 110 a and 110 b, the first set of third targetstructures 106 a and 106 b, the second set of third target structures112 a and 112 b, and/or the first set of fourth target structures 115 aand 115 b).

In Step 706, one or more overlay measurements are generated based on theone or more signals indicative of illumination emanating from the one ormore focus-sensitive metrology targets 100. For example, the controller204 may be configured to generate one or more overlay measurements ofthe sample based on one or more signals indicative of illuminationemanating from one or more portions of the sample (e.g., the first setof first target structures 102 a and 102 b, the second set of firsttarget structures 108 a and 108 b, the first set of second targetstructures 104 a and 104 b, the second set of second target structures110 a and 110 b, the first set of third target structures 106 a and 106b, the second set of third target structures 112 a and 112 b, and/or thefirst set of fourth target structures 115 a and 115 b). The one or moreoverlay measurements of the sample may correspond to an overlay positionof one or more layers of the sample. The controller 204 may beconfigured to generate one or more corrected overlay measurements bycorrecting one or more uncorrected overlay measurements (e.g., overlaymeasurements taken without regard to proper and/or desired focus) usingthe one or more focus-offset values. In this regard, the controller 204may be configured to provide one or more focus corrections determinedbased on the one or more focus-offset values to one or more portions ofthe one or more metrology tools 202, and the one or more metrology tools202 may be configured to generate additional metrology measurementsusing the corrected focus based on the one or more focus corrections.

In Step 708, one or more overlay errors of the sample are determined.For example, the controller 204 may be configured to determine one ormore overlay errors between two or more layers of the sample based onthe one or more overlay measurements of the sample.

In some embodiments, the method 700 may include one or more additionalsteps wherein one or more overlay corrections are provided based on theone or more overlay errors determined in at least Step 708. For example,the one or more additional steps may include the controller 204generating one or more control signals (or corrections to the controlsignals) for adjusting one or more parameters (e.g., fabricationsettings, configuration, and the like) of one or more process tools(e.g., lithographic tools). The control signals (or corrections to thecontrol signals) may be provided by the controller 204 as part of afeedback and/or feedforward control loop. The controller 204 may causethe one or more process tools to execute one or more adjustments to theone or more parameters of the one or more process tools based on the oneor more control signals (or corrections to the control signals). In someembodiments, the controller 204 may alert a user to make the one or moreadjustments. In this sense, the one or more control signals maycompensate for errors of one or more fabrication processes of the one ormore process tools, and thus may enable the one or more process tools tomaintain overlay within selected tolerances across multiple exposures onsubsequent samples in the same or different lots.

FIG. 8 illustrates a process flow diagram illustrating the steps of amethod 800 of forming a focus-sensitive metrology target 100, inaccordance with one or more embodiments of the present disclosure.

In Step 802, a first set of first target structures 102 a and 102 b isformed on one or more layers of a sample. For example, the first set offirst target structures 102 a and 102 b may be formed along ay-direction on the one or more layers of the sample, wherein the firstset of first target structures 102 a and 102 b may include a pluralityof segmented first pattern elements 103 a and 103 b. The plurality ofsegmented first pattern elements 103 a and 103 b may be configured foroverlay measurement along at least one measurement direction (e.g., ay-direction). The plurality of segmented first pattern elements 103 aand 103 b may be compatible with any metrology mode known in the art tobe suitable for the purposes contemplated by the present disclosure. Forexample, the one or more first pattern elements 103 a and 103 b may becompatible with a diffraction-based metrology mode (e.g., ascatterometry-based overlay (SCOL) metrology mode). In this regard, theone or more first pattern elements 103 a and 103 b may be configured toinclude periodic and/or segmented structures for metrology usingdiffraction-based metrology methods (e.g., grating-over-gratingstructures, or any structure known in the art to be suitable fordiffracting, scattering, and/or reflecting an illumination beam). By wayof another example, the one or more first pattern elements 103 a and 103b may be compatible with any image-based overlay metrology mode,including, without limitation, an advanced imaging metrology (AIM) mode,a box-in-box metrology mode, or any other metrology mode known in theart to be suitable for capturing an overlay signal (e.g., an image offocus-sensitive metrology target 100 features located on differentsample layers). It is noted that the plurality of segmented firstpattern elements 103 a and 103 b may include any one-dimensional ortwo-dimensional structure formed by any means known in the art,including, without limitation, one or more lithographic steps, one ormore direct etching steps, or the like. The first set of first targetstructures 102 a and 102 b and/or the plurality of segmented firstpattern elements 103 a and 103 b may be formed in any shape, including,without limitation, a square shape, a round shape, a rhombus-like shape,or a star-like shape. The first set of first target structures 102 a and102 b may be fabricated through one or more process steps such as, butnot limited to, one or more deposition, lithographic, or etching steps,and through the use of one or more process tools (e.g., lithographictools).

In Step 804, a first set of second target structures 104 a and 104 b isformed on one or more layers of a sample. For example, the first set ofsecond target structures 104 a and 104 b may be formed along ay-direction on the one or more layers of the sample, wherein the firstset of second target structures 104 a and 104 b may include a pluralityof segmented second pattern elements 105 a and 105 b. The plurality ofsegmented second pattern elements 105 a and 105 b may be toolsconfigured for overlay measurement along at least one measurementdirection (e.g., a y-direction). The plurality of segmented secondpattern elements 105 a and 105 b may be compatible with any metrologymode known in the art to be suitable for the purposes contemplated bythe present disclosure. For example, the one or more second patternelements 105 a and 105 b may be compatible with a diffraction-basedmetrology mode (e.g., a scatterometry-based overlay (SCOL) metrologymode). In this regard, the one or more second pattern elements 105 a and105 b may be configured to include periodic and/or segmented structuresfor metrology using diffraction-based metrology methods (e.g.,grating-over-grating structures, or any structure known in the art to besuitable for diffracting, scattering, and/or reflecting an illuminationbeam). By way of another example, the one or more second patternelements 105 a and 105 b may be compatible with any image-based overlaymetrology mode, including, without limitation, an advanced imagingmetrology (AIM) mode, a box-in-box metrology mode, or any othermetrology mode known in the art to be suitable for capturing an overlaysignal (e.g., an image of focus-sensitive metrology target featureslocated on different sample layers). It is noted that the plurality ofsegmented second pattern elements 105 a and 105 b may include anyone-dimensional or two-dimensional structure formed by any means knownin the art, including, without limitation, one or more lithographicsteps, one or more direct etching steps, or the like. The first set ofsecond target structures 104 a and 104 b and/or the plurality ofsegmented second pattern elements 105 a and 105 b may be formed in anyshape, including, without limitation, a square shape, a round shape, arhombus-like shape, or a star-like shape. The first set of second targetstructures 104 a and 104 b may be fabricated through one or more processsteps such as, but not limited to, one or more deposition, lithographic,or etching steps, and through the use of one or more process tools(e.g., lithographic tools).

In some embodiments, the method 800 may include a Step 806, wherein afirst set of third target structures 106 a and 106 b is formed on one ormore layers of a sample. For example, the first set of third targetstructures 106 a and 106 b may be formed along a y-direction on the oneor more layers of the sample, wherein the first set of third targetstructures 106 a and 106 b may include the plurality of segmented thirdpattern elements 107 a and 107 b. The plurality of segmented thirdpattern elements 107 a and 107 b may be configured for overlaymeasurement along at least one measurement direction (e.g., ay-direction). The plurality of segmented third pattern elements 107 aand 107 b may be compatible with any metrology mode known in the art tobe suitable for the purposes contemplated by the present disclosure. Forexample, the one or more third pattern elements 107 a and 107 b may becompatible with a diffraction-based metrology mode (e.g., ascatterometry-based overlay (SCOL) metrology mode). In this regard, theone or more third pattern elements 107 a and 107 b may be configured toinclude periodic and/or segmented structures for metrology usingdiffraction-based metrology methods (e.g., grating-over-gratingstructures, or any structure known in the art to be suitable fordiffracting, scattering, and/or reflecting an illumination beam). By wayof another example, the one or more third pattern elements 107 a and 107b may be compatible with any image-based overlay metrology mode,including, without limitation, an advanced imaging metrology (AIM) mode,a box-in-box metrology mode, or any other metrology mode known in theart to be suitable for capturing an overlay signal (e.g., an image offocus-sensitive metrology target 100 features located on differentsample layers). It is noted that the plurality of segmented thirdpattern elements 107 a and 107 b may include any one-dimensional ortwo-dimensional structure formed by any means known in the art,including, without limitation, one or more lithographic steps, one ormore direct etching steps, or the like. The first set of third targetstructures 106 a and 106 b and/or the plurality of segmented thirdpattern elements 107 a and 107 b may be formed in any shape, including,without limitation, a square shape, a round shape, a rhombus-like shape,or a star-like shape. The first set of third target structures 106 a and106 b may be fabricated through one or more process steps such as, butnot limited to, one or more deposition, lithographic, or etching steps,and through the use of one or more process tools (e.g., lithographictools).

In some embodiments, the method 800 may include a Step 808, wherein asecond set of first target structures 108 a and 108 b is formed on oneor more layers of a sample. For example, the second set of first targetstructures 108 a and 108 b may be formed along a x-direction on the oneor more layers of the sample, wherein the second set of first targetstructures 108 a and 108 b may include a plurality of segmented firstpattern elements 103 c and 103 d having the first pitch, the secondpitch, or the third pitch. The plurality of segmented first patternelements 103 c and 103 d may be configured for overlay measurement alongat least one measurement direction (e.g., an x-direction). The pluralityof segmented first pattern elements 103 c and 103 d may be compatiblewith any metrology mode known in the art to be suitable for the purposescontemplated by the present disclosure. For example, the one or morefirst pattern elements 103 c and 103 d may be compatible with adiffraction-based metrology mode (e.g., a scatterometry-based overlay(SCOL) metrology mode). In this regard, the one or more first patternelements 103 c and 103 d may be configured to include periodic and/orsegmented structures for metrology using diffraction-based metrologymethods (e.g., grating-over-grating structures, or any structure knownin the art to be suitable for diffracting, scattering, and/or reflectingan illumination beam). By way of another example, the one or more firstpattern elements 103 c and 103 d may be compatible with any image-basedoverlay metrology mode, including, without limitation, an advancedimaging metrology (AIM) mode, a box-in-box metrology mode, or any othermetrology mode known in the art to be suitable for capturing an overlaysignal (e.g., an image of focus-sensitive metrology target 100 featureslocated on different sample layers). It is noted that the plurality ofsegmented first pattern elements 103 c and 103 d may include anyone-dimensional or two-dimensional structure formed by any means knownin the art, including, without limitation, one or more lithographicsteps, one or more direct etching steps, or the like. The second set offirst target structures 108 a and 108 b and/or the plurality ofsegmented first pattern elements 103 c and 103 d may be formed in anyshape, including, without limitation, a square shape, a round shape, arhombus-like shape, or a star-like shape. The second set of first targetstructures 108 a and 108 b may be fabricated through one or more processsteps such as, but not limited to, one or more deposition, lithographic,or etching steps, and through the use of one or more process tools(e.g., lithographic tools).

In some embodiments, the method 800 includes a Step 810, wherein asecond set of second target structures 110 a and 110 b is formed on oneor more layers of a sample. For example, the second set of second targetstructures 110 a and 110 b may be formed along an x-direction on the oneor more layers of the sample, wherein the second set of second targetstructures 110 a and 110 b may include a plurality of segmented secondpattern elements 105 c and 105 d having the first pitch, the secondpitch, or the third pitch. The plurality of segmented second patternelements 105 c and 105 d may be configured for overlay measurement alongat least one measurement direction (e.g., an x-direction). The pluralityof segmented second pattern elements 105 c and 105 d may be compatiblewith any metrology mode known in the art to be suitable for the purposescontemplated by the present disclosure. For example, the one or moresecond pattern elements 105 c and 105 d may be compatible with adiffraction-based metrology mode (e.g., a scatterometry-based overlay(SCOL) metrology mode). In this regard, the one or more second patternelements 105 c and 105 d may be configured to include periodic and/orsegmented structures for metrology using diffraction-based metrologymethods (e.g., grating-over-grating structures, or any structure knownin the art to be suitable for diffracting, scattering, and/or reflectingan illumination beam). By way of another example, the one or more secondpattern elements 105 c and 105 d may be compatible with any image-basedoverlay metrology mode, including, without limitation, an advancedimaging metrology (AIM) mode, a box-in-box metrology mode, or any othermetrology mode known in the art to be suitable for capturing an overlaysignal (e.g., an image of focus-sensitive metrology target 100 featureslocated on different sample layers). It is noted that the plurality ofsegmented second pattern elements 105 c and 105 d may include anyone-dimensional or two-dimensional structure formed by any means knownin the art, including, without limitation, one or more lithographicsteps, one or more direct etching steps, or the like. The second set ofsecond target structures 110 a and 110 b and/or the plurality ofsegmented second pattern elements 105 c and 105 d may be formed in anyshape, including, without limitation, a square shape, a round shape, arhombus-like shape, or a star-like shape. The second set of secondtarget structures 110 a and 110 b may be fabricated through one or moreprocess steps such as, but not limited to, one or more deposition,lithographic, or etching steps, and through the use of one or moreprocess tools (e.g., lithographic tools).

In some embodiments, the method 800 includes a Step 812, wherein asecond set of third target structures 112 a and 112 b is formed on oneor more layers of the sample. For example, the second set of thirdtarget structures 112 a and 112 b may be formed along an x-direction onthe one or more layers of the sample, wherein the second set of thirdtarget structures 112 a and 112 b may include a plurality of segmentedthird pattern elements 107 c and 107 d having the first pitch, thesecond pitch, or the third pitch. The plurality of segmented thirdpattern elements 107 c and 107 d may be configured for overlaymeasurement along at least one measurement direction (e.g., anx-direction). The plurality of segmented third pattern elements 107 cand 107 d may be compatible with any metrology mode known in the art tobe suitable for the purposes contemplated by the present disclosure. Forexample, the one or more third pattern elements 107 c and 107 d may becompatible with a diffraction-based metrology mode (e.g., ascatterometry-based overlay (SCOL) metrology mode). In this regard, theone or more third pattern elements 107 c and 107 d may be configured toinclude periodic and/or segmented structures for metrology usingdiffraction-based metrology methods (e.g., grating-over-gratingstructures, or any structure known in the art to be suitable fordiffracting, scattering, and/or reflecting an illumination beam). By wayof another example, the one or more third pattern elements 107 c and 107d may be compatible with any image-based overlay metrology mode,including, without limitation, an advanced imaging metrology (AIM) mode,a box-in-box metrology mode, or any other metrology mode known in theart to be suitable for capturing an overlay signal (e.g., an image offocus-sensitive metrology target 100 features located on differentsample layers). It is noted that the plurality of segmented thirdpattern elements 107 c and 107 d may include any one-dimensional ortwo-dimensional structure formed by any means known in the art,including, without limitation, one or more lithographic steps, one ormore direct etching steps, or the like. The first set of second targetstructures 112 a and 112 b and/or the plurality of segmented thirdpattern elements 107 c and 107 d may be formed in any shape, including,without limitation, a square shape, a round shape, a rhombus-like shape,or a star-like shape. The second set of third target structures 112 aand 112 b may be fabricated through one or more process steps such as,but not limited to, one or more deposition, lithographic, or etchingsteps, and through the use of one or more process tools (e.g.,lithographic tools).

In some embodiments, the method 800 includes a Step 814 wherein a firstset of fourth target structures 115 a and 115 b is formed on one or morelayers of a sample. For example, the first set of fourth targetstructures 115 a and 115 b may be formed along a y-direction on the oneor more layers of the sample, wherein the first set of fourth targetstructures 115 a and 115 b may include a plurality of segmented fourthpattern elements 116 a and 116 b having a Moiré pattern. The pluralityof segmented fourth pattern elements 116 a and 116 b may be configuredfor overlay measurement along at least one measurement direction (e.g.,a y-direction). The plurality of segmented fourth pattern elements 116 aand 116 b may be compatible with any metrology mode known in the art tobe suitable for the purposes contemplated by the present disclosure. Forexample, the one or more fourth pattern elements 116 a and 116 b may becompatible with a diffraction-based metrology mode (e.g., ascatterometry-based overlay (SCOL) metrology mode). In this regard, theone or more fourth pattern elements 116 a and 116 b may be configured toinclude periodic and/or segmented structures for metrology usingdiffraction-based metrology methods (e.g., grating-over-gratingstructures, or any structure known in the art to be suitable fordiffracting, scattering, and/or reflecting an illumination beam). By wayof another example, the one or more fourth pattern elements 116 a and116 b may be compatible with any image-based overlay metrology mode,including, without limitation, an advanced imaging metrology (AIM) mode,a box-in-box metrology mode, or any other metrology mode known in theart to be suitable for capturing an overlay signal (e.g., an image offocus-sensitive metrology target features located on different samplelayers). It is noted that the plurality of segmented fourth patternelements 116 a and 116 b may include any one-dimensional ortwo-dimensional structure formed by any means known in the art,including, without limitation, one or more lithographic steps, one ormore direct etching steps, or the like. The first set of fourth targetstructures 115 a and 115 b and/or the plurality of segmented fourthpattern elements 116 a and 116 b may be formed in any shape, including,without limitation, a square shape, a round shape, a rhombus-like shape,or a star-like shape. It is further noted that the first set of fourthtarget structures 115 a and 115 b may allow the focus-sensitivemetrology target 100 to be used for more accurate overlay metrologymeasurements. For example, the inclusion of the first set of fourthtarget structures 115 a and 115 b with the first set of first targetstructures 102 a and 102 b, the first set of second target structures104 a and 104 b, and/or the first set of third target structures 106 aand 106 b may allow for additional metrology measurements based on oneor more signals emanating from the first set of first target structures102 a and 102 b, the first set of second target structures 104 a and 104b, the first set of third target structures 106 a, and/or the first setof fourth target structures 115 a and 115 b.

All of the methods described herein may include storing results of oneor more steps of the method embodiments in memory. The results mayinclude any of the results described herein and may be stored in anymanner known in the art. The memory may include any memory describedherein or any other suitable storage medium known in the art. After theresults have been stored, the results can be accessed in the memory andused by any of the method or system embodiments described herein,formatted for display to a user, used by another software module,method, or system, and the like. Furthermore, the results may be stored“permanently,” “semi-permanently,” temporarily,” or for some period oftime. For example, the memory may be random access memory (RAM), and theresults may not necessarily persist indefinitely in the memory.

It is further contemplated that each of the embodiments of the methoddescribed above may include any other step(s) of any other method(s)described herein. In addition, each of the embodiments of the methoddescribed above may be performed by any of the systems described herein.

One skilled in the art will recognize that the herein describedcomponents operations, devices, objects, and the discussion accompanyingthem are used as examples for the sake of conceptual clarity and thatvarious configuration modifications are contemplated. Consequently, asused herein, the specific exemplars set forth and the accompanyingdiscussion are intended to be representative of their more generalclasses. In general, use of any specific exemplar is intended to berepresentative of its class, and the non-inclusion of specificcomponents, operations, devices, and objects should not be taken aslimiting.

As used herein, directional terms such as “top,” “bottom,” “over,”“under,” “upper,” “upward,” “lower,” “down,” and “downward” are intendedto provide relative positions for purposes of description, and are notintended to designate an absolute frame of reference. Variousmodifications to the described embodiments will be apparent to thosewith skill in the art, and the general principles defined herein may beapplied to other embodiments

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations are not expressly set forth herein for sakeof clarity.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, other components. It isto be understood that such depicted architectures are merely exemplary,and that in fact many other architectures can be implemented whichachieve the same functionality. In a conceptual sense, any arrangementof components to achieve the same functionality is effectively“associated” such that the desired functionality is achieved. Hence, anytwo components herein combined to achieve a particular functionality canbe seen as “associated with” each other such that the desiredfunctionality is achieved, irrespective of architectures or intermedialcomponents. Likewise, any two components so associated can also beviewed as being “connected,” or “coupled,” to each other to achieve thedesired functionality, and any two components capable of being soassociated can also be viewed as being “couplable,” to each other toachieve the desired functionality. Specific examples of couplableinclude but are not limited to physically mateable and/or physicallyinteracting components and/or wirelessly interactable and/or wirelesslyinteracting components and/or logically interacting and/or logicallyinteractable components.

Furthermore, it is to be understood that the invention is defined by theappended claims. It will be understood by those within the art that, ingeneral, terms used herein, and especially in the appended claims (e.g.,bodies of the appended claims) are generally intended as “open” terms(e.g., the term “including” should be interpreted as “including but notlimited to,” the term “having” should be interpreted as “having atleast,” the term “includes” should be interpreted as “includes but isnot limited to,” and the like). It will be further understood by thosewithin the art that if a specific number of an introduced claimrecitation is intended, such an intent will be explicitly recited in theclaim, and in the absence of such recitation no such intent is present.For example, as an aid to understanding, the following appended claimsmay contain usage of the introductory phrases “at least one” and “one ormore” to introduce claim recitations. However, the use of such phrasesshould not be construed to imply that the introduction of a claimrecitation by the indefinite articles “a” or “an” limits any particularclaim containing such introduced claim recitation to inventionscontaining only one such recitation, even when the same claim includesthe introductory phrases “one or more” or “at least one” and indefinitearticles such as “a” or “an” (e.g., “a” and/or “an” should typically beinterpreted to mean “at least one” or “one or more”); the same holdstrue for the use of definite articles used to introduce claimrecitations. In addition, even if a specific number of an introducedclaim recitation is explicitly recited, those skilled in the art willrecognize that such recitation should typically be interpreted to meanat least the recited number (e.g., the bare recitation of “tworecitations,” without other modifiers, typically means at least tworecitations, or two or more recitations). Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,and the like” is used, in general such a construction is intended in thesense one having skill in the art would understand the convention (e.g.,“a system having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, and the like). In those instances where a convention analogousto “at least one of A, B, or C, and the like” is used, in general such aconstruction is intended in the sense one having skill in the art wouldunderstand the convention (e.g., “a system having at least one of A, B,or C” would include but not be limited to systems that have A alone, Balone, C alone, A and B together, A and C together, B and C together,and/or A, B, and C together, and the like). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

It is believed that the present disclosure and many of its attendantadvantages will be understood by the foregoing description, and it willbe apparent that various changes may be made in the form, constructionand arrangement of the components without departing from the disclosedsubject matter or without sacrificing all of its material advantages.The form described is merely explanatory, and it is the intention of thefollowing claims to encompass and include such changes. Furthermore, itis to be understood that the invention is defined by the appendedclaims.

What is claimed:
 1. A system comprising: one or more controllers havingone or more processors communicatively coupled to one or morefabrication tools, wherein the one or more processors are configured toexecute a set of program instructions maintained in memory, and whereinthe set of program instructions is configured to cause the one or moreprocessors to: receive, from one or more portions of the one or morefabrication tools, one or more signals indicative of illuminationemanating from a first set of first target structures and a first set ofsecond target structures of one or more focus-sensitive metrologytargets of a sample, wherein the one or more focus-sensitive metrologytargets of the sample comprise: the first set of first target structuresformed along a y-direction on one or more layers of the sample, thefirst set of first target structures comprising a plurality of segmentedfirst pattern elements; and the first set of second target structuresformed along the y-direction on one or more layers of the sample;determine one or more focus-offset values based on the one or moresignals indicative of illumination emanating from the first set of firsttarget structures and the first set of second target structures bytranslating the one or more signals indicative of illumination into afocus-offset value using a calibration curve; and provide one or morefocus corrections based on the one or more focus-offset values to one ormore portions of the one or more fabrication tools.
 2. The system ofclaim 1, wherein one or more metrology tools comprise at least: anillumination source; one or more illumination optics configured todirect an illumination beam from the illumination source onto one ormore portions of the one or more focus-sensitive metrology targets ofthe sample; and one or more projection optics configured to collectillumination reflected from the one or more portions of the one or morefocus-sensitive metrology targets of the sample; and one or moredetectors.
 3. The system of claim 1, wherein the segmented first patternelements and segmented second pattern elements each comprise a pluralityof pattern elements having at least one of a first pitch or a secondpitch, wherein the first pitch is greater than a resolution of one ormore portions of one or more metrology tools and the second pitch isless than the resolution of the one or more portions of the one or moremetrology tools.
 4. The system of claim 1, wherein the segmented firstpattern elements and segmented second pattern elements each comprise aMoiré pattern formed along the y-direction from overlapping periodicstructures on two layers of the sample, wherein periods of theoverlapping periodic structures are different.
 5. The system of claim 3,wherein the one or more focus-sensitive metrology targets furthercomprise: a second set of first target structures formed along anx-direction on one or more layers of the sample, the second set of firsttarget structures comprising a plurality of segmented first patternelements having at least one of the first pitch or the second pitch; asecond set of second target structures formed along the x-direction onone or more layers of the sample, the second set of second targetstructures comprising a plurality of segmented second pattern elementshaving at least one of the first pitch or the second pitch; and a secondset of third target structures formed along the x-direction on one ormore layers of the sample, the second set of third target structurescomprising a plurality of segmented third pattern elements having atleast one of the first pitch, the second pitch, or a third pitch.
 6. Thesystem of claim 4, wherein the one or more focus-sensitive metrologytargets further comprise: a first set of third target structures formedon one or more layers of the sample, the first set of third targetstructures comprising a plurality of segmented third pattern elements,the plurality of segmented third pattern elements comprising a Moirépattern formed along the y-direction from overlapping periodicstructures on two layers of the sample, wherein periods of theoverlapping periodic structures are different; and a first set of fourthtarget structures formed on one or more layers of the sample, the firstset of fourth target structures comprising a plurality of segmentedfourth pattern elements, the plurality of segmented fourth patternelements comprising a Moiré pattern formed along the y-direction fromoverlapping periodic structures on two layers of the sample, whereinperiods of the overlapping periodic structures are different.
 7. Thesystem of claim 1, wherein the one or more fabrication tools comprise atleast one of an extreme ultraviolet (EUV) scanner or one or morelithographic tools.
 8. The system of claim 1, wherein the samplecomprises a semiconductor wafer.